At 19.25 hours on 14 October 1944, U-1223 fired a spread of two torpedoes at the convoy ONS-33G in Gulf of St.Lawrence and hit the HMCS Magog (Lt. Lewis Dennis Quick, RCNR) with one torpedo in the stern. At 19.30 hours, a Gnat was fired, which detonated in the wake of the Canadian frigate HMCS Toronto (A/Lt.Cdr. H.K. Hill, RCNVR) without damaging the vessel. HMCS Magog lost 65 feet of her stern, three men were killed and three injured. The ship was first taken in tow by the HMCS Toronto and later taken over by a tug and towed to Quebec City, where the ship was declared a total loss. She was decommissioned on 20 December 1944.